A simple scheme has been developed for confirming the phenotype of the standard set of Salmonella typhimurium tester strains. This scheme employs a series of filter paper discs impregnated with diagnostic mutagens or bacterial toxins. Up to 6 diagnostic discs can be placed on a petri dish to test a single Salmonella strain. The Salmonellae are distinguished by their responses to ampicillin, crystal violet, nitrofurantoin, 9- aminoacridine, 4-nitro-o-phenylenediamine and sodium azide. The discs have maintained their reactivity in storage for 13 months.